1. Field of the Invention
The present invention relates to a fusing apparatus. More particularly, the present invention relates to a fusing roller which maximizes the induced heating efficiency of a heating portion by making the heating unit firmly contact an object to be heated and then concentrating magnetic flux on the object to be heated, and a fusing apparatus having the fusing roller.
2. Description of the Related Art
In general, electrophotographic image forming apparatuses, such as laser printers or digital copiers, print a unicolored or multicolored image by applying light to a photosensitive medium charged with predetermined potentials to form a latent electrostatic image on the photosensitive medium, enabling a developer to develop the latent electrostatic image with a predetermined color of toner, transferring the developed toner image to a sheet of paper, and then fusing the transferred image onto the sheet of paper.
Electrophotographic printing apparatuses are classified as either wet-type electrophotographic printing apparatuses or dry-type electrophotographic printing apparatuses according to the type of developing agent that they use. Wet-type electrophotographic printing apparatuses use a developing agent in which toner particles are diffused into a liquid carrier, whereas dry-type electrophotographic printing apparatuses use a homogenous developing agent which is comprised of toner particles, or a heterogeneous developing agent which is a mixture of carrier particles and toner particles.
FIG. 1 is a latitudinal cross-sectional view schematically illustrating a conventional fusing apparatus 10 using a halogen lamp as a heat source, and FIG. 2 is a longitudinal cross-sectional view of the conventional fusing apparatus of FIG. 1, taken along line I-I″ of FIG. 1. Referring to FIGS. 1 and 2, the fusing apparatus 10 includes two fusing rollers 11 and 12, which are formed as aluminum cylinders. Both ends of each of the fusing rollers 11 and 12 are supported by bearings 14, and the fusing rollers 11 and 12 are installed to become in contact with each other along longitudinal directions thereof. A coating layer 13 is formed on the surface of each of the fusing rollers 11 and 12. The coating layer 13 forms a nip, via which heat is transferred from each of the fusing rollers 11 and 12 to a toner image 21 on a recording medium 20, and which helps each of the fusing rollers 11 and 12 to be easily detached from the toner image 21 fused onto the recording medium 20.
A heating portion 15 is installed at the center of each of the fusing rollers 11 and 12 and uses, as a heat source, a halogen lamp that emits heat when connected to an external power supply (not shown). The heating portion 15 is separated from the inner surface of each of the fusing rollers 11 and 12 by an empty space therebetween filled with air.
When a current supplied by the external power supply is applied to both ends of the heating portion 15, the heating portion 15 generates radiant energy. The radiant energy is transmitted to the inner surface of each of the fusing rollers 11 and 12 via air and is then converted into thermal energy passing through a light-heat conversion layer, which is formed of a black body. The thermal energy is then conducted to the nip, which is an interface between the fusing rollers 11 and 12, via the fusing rollers 11 and 12 and the coating layer 13, and is transmitted to the toner image 21 on the recording medium 20 so that the toner image 21 can be fused onto the recording medium 20 by the thermal energy.
However, the conventional fusing apparatus using such a halogen lamp as a heat source has the following disadvantages.
First, since a halogen lamp has a low thermal efficiency, a considerable amount of time is required for warming the halogen lamp until the temperature of the halogen lamp reaches a desired fusing temperature. Therefore, a user has to wait until the halogen lamp is heated to the desired fusing temperature and the conventional fusing apparatus becomes ready to print documents.
Second, since the halogen lamp is separated from the inner surface of each of the fusing rollers 11 and 12 by the empty space therebetween filled with air, heat emitted from the halogen lamp heats each of the fusing rollers 11 and 12 through radiation and passes through the fusing rollers 11 and 12 through conduction. Thus, the speed of transmitting heat from the halogen lamp to the fusing rollers 11 and 12 is relatively low, and the thermal efficiency of the conventional fusing apparatus is also low.
Accordingly, a need exists for a system and method for improving thermal transmission and efficiency in a fusing apparatus, while reducing the time required for warming the fusing apparatus to a target temperature.